Piezoelectric pressure transducer



Sept. 22, 1964 F. PlscHlNGER 3,150,274

PIEZOELECTRIC PRESSURE TRANSDUCER Filed sept. so, 1960 B H5772 /OLISC[nger #LZ/L United States Patent O 3,150,274 PIEZOELECTRIC PRESSURETRANSDUCER Franz Pischnger, Graz, Austria, assignor to Hans List, Graz,Austria Filed Sept. 30, 1960, Ser. No. 59,732 Claims priority,application Austria Oct. 2, 1959 2 Claims. (Cl. S10-8.9)

The invention relates to a piezoelectric gauge, in particular formeasuring the pressure in the cylinders of internal combustion engines,comprising a casing and a sleeve attached thereto, said sleevepresenting a thin- Walled elastic enclosure for the piezoelernents atleast in the area of the pressuredoaded extremity and being closed :atsaid extremity by a pressure-transfer head, an annular chamber beingprovided between said sleeve and said casing, said annular chamber beingclosed by a membrane at the head end and traversed by the coolantentering through an inlet and discharged through an outlet opening.

In conventional `appliances of this type, the cooling water is deliveredto the annular chamber through a duct', said cooling water ilowingaround the sleeve and emerging from the annular chamber through adischarge duct located lapproximately opposite the `admission duct.Experience goes to show that precisely such elements of thepiezoelectric gauge which attain the highest temperature in operation,that is in particular, the sleeve and the pressure-transfer head areinadequately cooled. As a result, these elements are subject to anexcessive thermal stress and the temperature of the quartz crystalsgenerally used as piezoelements is not maintained on a constant level,so that measurements become inaccurate. ln addition, it was found thatthe water which is inadequately entrained by the current, especially inthe vicinity of the membrane, will start boiling, thereby causing themembrane to vibrate. These vibrations are transferred to thepiezoelements causing errors of measurement such as overlapping of thepressure curve recorded by a cathode r-ay oscillograph.

The purpose of the invention is to eliminate these drawbacks, the basicidea being to provide for a satisfactory heat evacuation by dissipatingthe heat already on its way to the piezoelernents from thepressure-loaded extremity of the sleeve and in particular, from the headwhich closes the latter on the pressure side.

The invention consists in providing the head in the area of the annularchamber with at least one through bore extending in transverse relationtoI the sleeve and serving for the passage of the cooling liquid, andfurthermore arranging inside the Kannular chamber two approximatelydiametrically opposite projecting ribs extending axially over the entirelheight of the annular chamber, said ribs originating on the outersurface of the annular chamber and protruding towards the sleeve, theinlet and outlet openings being located at diiierent sides of theprojecting ribs. The design according to the invention provides apositive iiow of the cooling liquid inside the annular cooling chamberof the piezoelectric gauge, thereby preventing the heat from ilowingfrom the front end of the piezoelectric gauge to the piezoelements. As aresult of the considerably improved cooling effect, the piezoelectriceiiciency will not be impaired by temperature tluctuations of thepiezoelements. The projecting ribs which may extend nearly to the outersurface of the sleeve deflect a substantial portion of the coolingliquid entering the annular chamber through the inlet opening bydischarging same through the bores in the pressure-transfer head,thereby keeping the cooling liquid permanently on the move in everysection of the `annular chamber. This largely eliminates the risk of thecooling liquid starting boiling, particularly in the area of themembrane which closes the annular chamber. Besides, the piezoelementsare located farther inside the piezoelectric gauge, since on account ofthe provision of bores, the head is of greater length without anynoticeable increase of its mass. The coolant used may be either water ora liquid having a higher boiling point than water, such as silicon oil.

lt is already known to cool the pressure-loaded eX- tremity of thesleeve of the piezoelectric gauge by means of cooling water in permanentmotion. According to that design, the piezoelements are located outsidethe sleeve, surrounding the latter inside an annular casing encompassedby an external cooling chamber of annular shape. ln addition to thisexternal cooling circuit, an internal cooling circuit serves to cool thesleeve, the cooling water being delivered through a pipe extending intothe interior of the sleeve nearly to the pressure-loaded extremity ofthe latter and drained oi alongside the Walls of the sleeve. However,this arrangement implies a most complicated design ot the piezoelectricgauge Without improving the cooling elect to any considerable extent, asonly a minor portion of the sleeve surface is covered by the coolingwater and only a negligible section of the head closing the sleeve atthe pressure end cornes into contact with the cooling water.

According to another known design it has been proposed to provide themembrane of a capacity-operated piezoelectric gauge with transversegrooves on the underside, a disk pressed against said membrane deliningin conjunction with said grooves, ducts for the passage of the coolant.In view of the particular nature of the physical phenomena applied inthis design, there are no piezoelements nor is there any elementcomparable to the pressure-transfer head of the object of the invention.Moreover, no provision has been made for the maintenance of a regularcurrent so that the flow of coolant through the passages defined by thetransverse grooves in the membrane is wholly inadequate.

According to a preferred embodiment of the invention, the projectingribs are formed by a guide sleeve, the outer surface of which adjoinsthe casing and which extends over the entire height ofthe annularchamber. The most remarkable feature of this embodiment resides in thefact that it is easy to manufacture. The difficulty of installing andremoving the sleeve if the projecting ribs are rigidly attached to thecasing is also eliminated.

An embodiment of the invention is illustrated by the accompanyingdrawing in which FIGURE 1 shows a front view of the piezoelectric gaugeaccording tothe invention,

FIGURE 2 is a plan View of same,

FIGURE 3 is a cross-sectional view of the portion ot the piezoelectricgauge containing the piezoelernents, on line lll-Ill of FlGURE 4, and

FlGURE 4 is a cross-sectional view on line IV-lV of FIGURE 3, each on anenlarged scale.

The piezoelectric gauge illustrated comprises a cylindrical casing l,the lower extremity of which presents a threaded connection Z suitablefor screwing it into the cylinder head of an internal combustion enginefor example, whereas its upper extremity presents a hexagon head 3. Theupper extremity of the casing 1 also carries pipes l and 5 to beconnected to the inlet and discharge ducts for the coolant and aleading-in insulator 6 from which the electrical supply line emerges.

The sleeve 7 is located inside the casing 1 and attached thereto andclosed by a pressure-transfer head S. In the area of its pressure-loadedextremity the sleeve 7 is thinwalled and elastic and encloses thepiezoelements, such as, for example, two quartz crystals 9 and 10. Inthe embodiment shown, these are superimposed and connected inopposition, an electrode l1 being provided between them for the purposeof leaking oit the positive charges 3 for instance, whereas the negativecharges are allowed to leak olf over the body of the piezoelectricgauge. For that purpose an electrode 12 is provided on one side of thequartz crystals and a steel cylinder 13 on the other side, said cylinderbeing connected to the quartz crystal 9 and serving at the same time toclamp the quartzes downA The electrode 12y adjoining the quartz crystal19 is conductively connected with'the head S and consequently also withthe body of the piezoelectric gauge via a layer 14 of a soft metal suchas aluminum. The purpose of the metal layer is to establish an electriccontact with the least possible transfer resistance between theelectrode 12 and the head 8. lnside the steel cylinder 13 an insulatingtube 15 is located which encloses the electric wire 16 leading from theelectrode 11 outside.

Recessed between the thin-walled section of the sleeve enclosing thepiezoelectric quartz crystals 9 and 1G and the casing 1 is an annularchamber 17 closed at the head end by a membrane 18 located between thecasing 1 and the head 3, said membrane being maintained in position byrings 19 and 29. The upper part of the annular chamber 17 comprises aninlet 21 and an outlet 22 through which the coolant admitted throughpipe 4 and discharged through pipe 5 and Via channels 23 in the casing 1ows through the annular chamber 17.

The section of the head 8 located in the yarea of the annular chamber 17comprises three through bores 24 extending in transverse relation to thesleeve, for the passage of the cooling liquid from one half of theannular chamber 17 to the other half. In order to get the largestpossible amount of cooling liquid to ilow through the bores 24, a guide`sleeve 25 is provided in the annular chamber, said guide sleeveadjoining with its outer surface the casing 1 and extending over theentire height of the annular chamber 1'7. The guide sleeve 25 comprisestwo diametrically opposite projecting ribs 26 and 27 extending in axialdirection and protruding towards the thin-walled section of sleeve 7.Between the projecting ribs 26 and 27 on the one hand and thethin-walled section of sleeve 7 on the other hand, only narrow slots areleft for'the passage of the cooling liquid. Thus a larger or smallerportion of the cooling liquid is allowed to iiow through the bores Z4 inthe head 8, depending on the width of said slots. In order to achieve agreater cooling elect the rojecting ribs 26 4and 27 are for example,dimensioned in such a way'as to let about 6G percent of the coolingliquid pass through the bores 24.

I claim:

l. A piezoelectric pressure transducer comprising a casing and a sleeveclamped in said casing, iezoelcctric elements `enclosed in said sleeve,a head closing said sleeve at its pressure-loaded extremity fortransferring pressure to said piezoelectric elements, said sleeve beingthinwalled and elastic at least in -a portion thereof enclosing saidpiezoelectric elements, a guide sleeve enclosed by said casing andcoaxial with and spaced from said firstrnen-tioned sleeve, the spacebetween the sleeves forming an annular chamber surrounding thethin-walled portion of the rst-mentioned sleeve, a membrane closing saidannular chamber, said guide sleeve having inlet and outlet openings forthe admission and discharge of a cooling liquid to and from the annularchamber, said head having a bore traversing said head in the area of theannular chamber and serving for the passage of the cooling liquid, twoaxially extendingand diametrically opposite projecting ribs in theannular chamber, said projecting ribs being integral with the said guidesleeve but freely protruding towards the inst-mentioned sleeve andextending over the entire height of the annular chamber, and said inletand outlet openings being located on opposite sides of the projectingribs. i

2. A piezoelectric gauge as claimed in claim l, Vin which a plurality ofbores are provided inside the head in parallel relation to each other.

References Cited in the tile of this patent UNITED STATES PATENTS2,439,047 Grinstead et al Apr. 6, 1948 2,507,636 Kistler May 16, 19502,896,138 Grinstead July 21, 1959 2,976,466 Grinstead Mar. 21, 1961FOREIGN PATENTS 922,183 France Q lan. 27, 1947 660,182 Great BritainOct. 31, 1951 1,031,155 France Mar. 18, 1953

1. A PIEZOELECTRIC PRESSURE TRANSDUCER COMPRISING A CASING AND A SLEEVECLAMPED IN SAID CASING, PIEZOELECTRIC ELEMENTS ENCLOSED IN SAID SLEEVE,A HEAD CLOSING SAID SLEEVE AT ITS PRESSURE-LOADED EXTREMITY FORTRANSFERRING PRESSURE TO SAID PIEZOELECTRIC ELEMENTS, SAID SLEEVE BEINGTHINWALLED AND ELASTIC AT LEAST IN A PORTION THEREOF ENCLOSING SAIDPIEZOELECTRIC ELEMENTS, A GUIDE SLEEVE ENCLOSED BYS SAID CASING ANDCOAXIAL WITH AND SPACED FROM SAID FIRSTMENTIONED SLEEVE, THE SPACEBETWEEN THE SLEEVES FORMING AN ANNULAR CHAMBER SURROUNDING THETHIN-WALLED PORTION OF THE FIRST-MENTIONED SLEEVE, A MEMBRANE CLOSINGSAID ANNULAR CHAMBER, SAID GUIDE SLEEVE HAVING INLET AND OUTLET OPENINGSFOR THE ADMISSION AND DISCHARGE OF A COOLING LIQUID TO A FROM THEANNULAR CHAMBER, SAID HEAD HAVING A BORE TRAVERSING SAID HEAD IN THEAREA OF THE ANNULAR CHAMBER AND SERVING FOR THE PASSAGE OF THE COOLINGLIQUID, TWO AXIALLY EXTENDING AND DIAMETRICALLY OPPOSITE PROJECTING RIBSIN THE ANNULAR CHAMBER, SAID PROJECTING RIBS BEING INTEGRAL WITH THESAID GUIDE SLEEVE BUT FREELY PROTRUDING TOWARDS THE FIRST-MENTIONEDSLEEVE AND EXTENDING OVER THE ENTIRE HEIGHT OF THE ANNULAR CHAMBER, ANDSAID INLET AND OUTLET OPENINGS BEING LOCATED ON OPPOSITE SIDES OF THEPROJECTING RIBS.